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SAMJ: South African Medical Journal

On-line version ISSN 2078-5135
Print version ISSN 0256-9574

SAMJ, S. Afr. med. j. vol.99 n.6 Pretoria Jun. 2009

 

  • DWI-ADC score 5 assigns a definitive PI-RADS score of 4.

  • Central zone interpretation

    A normal CZ is seen in 93% of MRI studies.1 It is recognised as low T2 signal intensity tissue surrounding the ejaculatory ducts, posterior to the TZ at the prostatic base, coursing medially to the urethra at the level of the verumontanum. The CZ is normally symmetrical and at high b-value DWI, is symmetrically mildly hyperintense. It does not demonstrate early enhancement on DCE images and has Type 1 enhancement.1 See Figure 8.

    Key pointers

    Symmetry at base level:

    • Can be compressed by the TZ (especially if hyperplastic) posteriorly.

    • 'Teardrop' or 'moustache' shape.1

    Beware: can appear asymmetric in 18%.1

    Prostate cancer can occur in the CZ in 5%. It tends to be more aggressive with a higher grade and increased incidence of EPE and seminal vesicle invasion.1

    Suspect tumour when there is asymmetry, and the lesion extends beyond the verumontanum, especially if there is a mass-like change. Dynamic contrast enhanced imaging is helpful. Central zone tumours demonstrate early enhancement with type 3 (wash-out) curves, compared to the normal CZ which has a type 1 wash-out curve, that is, progressive enhancement.1,11,12

    Anterior fibromuscular stroma interpretation

    Normal AFMS has a bilaterally symmetric shape (crescentic) and symmetrically low SI (equivalent to SI of the pelvic floor muscles) on T2W, ADC and high b-value DWI, that is, 'low on all sequences'.1 See Figure 9.

     

     

    Prostate cancer does not arise in the AFMS but extends from either the PZ or the TZ. Abnormalities in the AFMS with increased SI and restricted diffusion when compared with pelvic floor muscles, asymmetric enlargement or a focal mass, increases the suspicion for tumour from the adjacent PZ or TZ. Determine (may not always be possible) from where the tumour most likely arises and apply the scoring criteria for that area.1

    Assessment of extra-prostatic extension

    • Frank capsular breech by a suspicious lesion.

    • Must include possible invasion of rectum and bladder.

    • Broad capsular contact (10 mm - 20 mm).

    • Bulging capsule.

    • Irregular, spiculated, angular prostate margin adjacent to tumour.

    • Asymmetry, traction, thickening of neuro-vascular bundles.

    • Seminal vesicle invasion - asymmetric loss of normal T2 hyperintensity in the seminal vesicle lumen.

     

    Pitfalls

    An extruded hyperplastic nodule from the TZ into the PZ, can masquerade as a PZ lesion.

    A neurovascular bundle that is close to the capsule or projects into the PZ with false restriction of diffusion can be falsely interpreted as a possible PZ lesion. Prostatitis can be falsely interpreted as a PZ lesion. Atypical anatomy of the central zone can masquerade as a lesion.

     

    Reporting template

    See Figure 10 - a template for reporting of multiparametric prostate MRI studies using the algorithm outlined in Figure 11, providing the reporting radiologist with a structured approach to lesions of the peripheral and transitional zones of the prostate.

     

     

    Summary

    Prostate Imaging-Reporting and Data System v2 is being widely utilised in clinical practice. Worldwide experience has highlighted the areas of ambiguity, poor performance and reduced inter-observer variability, necessitating the upgrade to PI-RADS v2.1, which addresses these issues. There are some minor modifications including a simplified scoring system whilst maintaining the framework for acquisition and interpretation. This fine tuning of a well-established diagnostic imaging system further improves the stratification of risk in patients with suspected prostatic carcinoma. As mpMRI becomes more widely available in developing countries it is expected that the use of risk stratification models, such as PI-RADS will increase. The reporting radiologist who is able to apply the framework of PI-RADS in daily practice will be well-positioned to contribute to the multi-disciplinary management of patients with prostate carcinoma.

     

    Acknowledgements

    Dr Gareth Bydawell for assistance with selection of MRI images for classification of lesions.

    Competing interests

    The authors declare that they have no financial or personal relationships that may have inappropriately influenced them in writing this pictorial review.

    Authors' contributions

    R.S. was the guarantor of integrity of the entire study, performed the literature search, wrote the manuscript and selected patients. S.K.M. was the principal promoter and reviewer of the manuscript, designed and annotated all the images and tables. S.K.M., E.N. and D.C.M. all reviewed the manuscript and made key concept additions. All the authors read and agreed on the final article.

    Ethical considerations

    This article followed all ethical standards for research.

    Funding information

    This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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